1. Field of the Invention
The present invention relates to a waveguide/strip line converter, which converts electric power in a microwave or millimeter wave band.
2. Description of Related Art
A waveguide/strip line converter conventionally includes a short-circuiting layer (a metal layer), a matching element, and a dielectric substrate (e.g., JP-2000-244212-A (corresponding to U.S. Pat. No. 6,580,335)). The short-circuiting layer has a slit, which is disposed at an opening of a waveguide. The matching element is disposed on an inner side of the waveguide, and the short-circuiting layer and the matching element are disposed generally parallel to each other with a predetermined gap formed therebetween. The dielectric substrate is provided in this predetermined gap. The matching element and a strip line, which is formed in the slit of the short-circuiting layer, are electromagnetically connected as a result of disposing them close to each other. A conversion of electric power by means of this electromagnetic connection of the matching element and the strip line eliminates the use of a short-circuiting waveguide block.
According to the above conventional art, a high frequency circuit is arranged on the substrate on which the strip line is formed. When a power supply line to drive the high frequency circuit is formed on the same substrate on which the strip line is formed, an electric current circulating through the power supply line sometimes has an influence on the strip line. The influence on the strip line can be reduced, for example, by including a multilayer substrate in the converter, and by forming the power supply line on a different substrate from the substrate on which the strip line is formed.
When the converter includes the multilayer substrate, a waveguide passage, through which a radio wave propagates, is formed between the strip line and the matching element. For instance, due to a positional shift, which is generated between adjacent substrates while the multilayer substrate is being produced, the waveguide passage on a lower layer side of a grounding metal pattern of the strip line protrudes into an inner side of the waveguide passage that is formed on the grounding metal pattern. As a result, a resonance characteristic of the matching element, that is, a characteristic of the converter deteriorates.